Mac Overlays: Allow multiple overlays with sandwich strategy

cc/output/overlay_strategy_single_on_top.cc

Index: cc/output/overlay_strategy_single_on_top.cc
diff --git a/cc/output/overlay_strategy_single_on_top.cc b/cc/output/overlay_strategy_single_on_top.cc
index 5670a37f93de2dd06b023a377608406f11b05875..a55816d8237a52e4c1e4fecd697f8b3c2265e415 100644
--- a/cc/output/overlay_strategy_single_on_top.cc
+++ b/cc/output/overlay_strategy_single_on_top.cc
@@ -13,7 +13,7 @@ namespace cc {
 
 OverlayStrategySingleOnTop::~OverlayStrategySingleOnTop() {}
 
-bool OverlayStrategySingleOnTop::TryOverlay(
+QuadList::Iterator OverlayStrategySingleOnTop::TryOverlay(
     OverlayCandidateValidator* capability_checker,
     RenderPassList* render_passes_in_draw_order,
     OverlayCandidateList* candidate_list,
@@ -34,7 +34,7 @@ bool OverlayStrategySingleOnTop::TryOverlay(
         &overlap_rect);
     if (rect.Intersects(overlap_rect) &&
         !OverlayStrategyCommon::IsInvisibleQuad(*overlap_iter))
-      return false;
+      return quad_list.end();

[ccameron, 2015/09/02 22:22:33]

This shouldn't return the end() iter -- we want to keep trying!

   }
 
   // Add our primary surface.
@@ -53,10 +53,11 @@ bool OverlayStrategySingleOnTop::TryOverlay(
   // If the candidate can be handled by an overlay, create a pass for it.
   if (candidates[1].overlay_handled) {
     quad_list.EraseAndInvalidateAllPointers(candidate_iterator);
+    DCHECK(candidate_list->empty());
     candidate_list->swap(candidates);

[ccameron, 2015/09/02 22:22:33]

here we want to return STOP -- this strategy only allows 1 overlay.

-    return true;
   }
-  return false;
+
+  return quad_list.end();

[ccameron, 2015/09/02 22:22:33]

likewise about keeping trying.

 }
 
 }  // namespace cc